In recent years, investigations are made to recycle spent resin materials from the standpoint of environmental protection. If a paint film is formed on the surface of the spent resin materials, when the resin materials are processed for recycling, the resin materials are contaminated by the paint film, resulting in great reduction in mechanical properties of the resin materials. Therefore, it is necessary to previously remove the paint film from the surface of the resin materials prior to process for recycling. For this reason, in recycling resin materials having a paint film formed on the surface thereof, proposals have been made for a method of removing a paint film by shot blasting, a method of melting the resin materials with an extrusion molding machine and filtering the molten resins through a filter to remove a paint film, or a method of rolling the resin materials using rolls and the like and removing a paint film by shearing action due to circumferential speed difference between rolls, as disclosed in, for example, Japanese Laid-open Patent Application 7-214558 and Japanese Laid-open Patent Applications 7-256640, 7-256641, 7-256642 and 7-256643.
However, when removing the paint film by the methods as described above, there arises the following problems:
(1) Shot blasting method
a) If a molding shape of the resin material is complicated, it is difficult to uniformly remove the paint film, thereby taking much time.
b) If shot used in blasting is increased in order to enhance processing efficiency, the resin material burns, resulting in deterioration of quality of the resin material, or the blast is embedded in the resin material, causing contamination with foreign materials.
(2) Filtration method with filter
a) If a filter having fine mesh is used, the paint film is substantially removed, but if the paint film has a small thickness, the elongated cut paint film may not be filtered off, resulting in contamination with such a paint film.
b) Since it takes much time for filtration, if its extrusion force is increased, excessive compression load is applied to the resin material, resulting in deterioration of the resin material.
(3) Rolling method with rolls
Since the rolling is conducted at a temperature of less than 70.degree. C., such a temperature is too low to deform the resin material. Therefore, it is difficult to introduce the resin material into the rolls, and also the resin material may not sufficiently be deformed by the rolls. For this reason, the resin material must be flattened with a specific press, or the resin material must be finely divided so as to relatively increase flat portions, thus requiring complicated procedures and taking much time.